Some previous microscope stages have used gear drive or rack and pinion systems to position a microscope stage. See, for example, U.S. Pat. No. 3,826,559 issued to Berliner, et al. on July 30, 1974 and entitled "Adjustable Tension Control Means for Microscopes" and also U.S. Pat. No. 3,572,888 issued to Takashi Kawashima on Mar. 30, 1971, and entitled "Rotary and Transversely Adjustable Microscope Stage."
Typically, these systems have the disadvantage that the larger the size of the gears used in the system, the more backlash there is in the adjustment of the stage and instability at the adjusted position. Such backlash is caused by the greater the tolerances allowable in the meshing of the gears, and hence the position of the sample platform may vary without any corresponding change in the position of the associated controls.
Alternatively, a gear system having very fine-toothed gears is frequently damaged when the stage is overdriven, i.e., driven to its full extension along one axis. Overdriving the stage is common since the operator is typically not looking directly at the stage controls during the adjustment operation.
Other adjustment techniques include screw drive and micrometer drive techniques. See, for example, U.S. Pat. No. 3,652,146 entitled "Precision Microscope Stage" and issued to David Sydney George on Mar. 28, 1972, and also U.S. Pat. No. 3,525,140 entitled "Micro-Motion Device" and issued to R. P. Cachon, et al. on Aug. 25, 1970. These techniques presented problems similar to those discussed above.
In accordance with the preferred embodiment of the present invention, drive bars, each having a tapered longitudinal edge, are movably mounted to the sample platform and base plate of a mensuration stage. The base is fixedly mounted to the frame of the microscope or other apparatus. The tapered edge of the drive bars each frictionally engage a V-grooved drive wheel, each of which drive wheels being axially mounted to an intermediate plate of the stage and coaxially coupled to rotatably operable controls. Rotation of one of the controls drives only the platform along one axis. Rotation of the other control knob drives the intermediate plate, which is coupled to the sample platform, along the other axis. Thus, co-planar, X-Y positioning of the sample platform is provided. Leaf-springs formed in the ends of the drive bars urge the tapered edge of the drive bars into the groove of the drive wheels, thus enhancing the frictional engagement therebetween. In addition, each end of the tapered edges of the drive bars are shaped to cause the drive bar to frictionally disengage from the drive wheel as the sample platform is driven to its limit in either direction along either axis.